Remove self-assignments

[Marc Glisse]

Hello,

this patch removes some self-assignments. I don't know if this is the best 
way, but it passes a bootstrap and the testsuite on x86_64-linux-gnu.

2013-06-10  Marc Glisse  <marc.gli...@inria.fr>

        PR tree-optimization/57361
gcc/
        * tree-ssa-dse.c (dse_possible_dead_store_p): Handle self-assignment.

gcc/testsuite/
        * gcc.dg/tree-ssa/pr57361.c: New file.

--
Marc GlisseIndex: testsuite/gcc.dg/tree-ssa/pr57361.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/pr57361.c (revision 0)
+++ testsuite/gcc.dg/tree-ssa/pr57361.c (revision 0)
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-dse1-details" } */
+
+struct A { int x; double y; };
+void f (struct A *a) {
+  *a = *a;
+}
+
+/* { dg-final { scan-tree-dump "Deleted dead store" "dse1"} } */

Property changes on: testsuite/gcc.dg/tree-ssa/pr57361.c
___________________________________________________________________
Added: svn:keywords
   + Author Date Id Revision URL
Added: svn:eol-style
   + native

Index: tree-ssa-dse.c
===================================================================
--- tree-ssa-dse.c      (revision 199867)
+++ tree-ssa-dse.c      (working copy)
@@ -77,20 +77,29 @@ static void dse_enter_block (struct dom_
    Return TRUE if the above conditions are met, otherwise FALSE.  */
 
 static bool
 dse_possible_dead_store_p (gimple stmt, gimple *use_stmt)
 {
   gimple temp;
   unsigned cnt = 0;
 
   *use_stmt = NULL;
 
+  /* Self-assignments are zombies.  */
+  if (gimple_assign_rhs_code (stmt) == TREE_CODE (gimple_assign_lhs (stmt))
+      && operand_equal_p (gimple_assign_rhs1 (stmt),
+                         gimple_assign_lhs (stmt), 0))
+    {
+      *use_stmt = stmt;
+      return true;
+    }
+
   /* Find the first dominated statement that clobbers (part of) the
      memory stmt stores to with no intermediate statement that may use
      part of the memory stmt stores.  That is, find a store that may
      prove stmt to be a dead store.  */
   temp = stmt;
   do
     {
       gimple use_stmt, defvar_def;
       imm_use_iterator ui;
       bool fail = false;